The adjustable idler gear is a straight-cut gear, mounted on a bushing pressed into the center of the gear, which in turn is supported on a stationary hub. The hub is secured to the gear case by a retaining plate, three studs, and locknuts. The studs are pressed into the gear case from the rear, and the flanged locknuts are installed after the gear, hub and hub retaining plate are installed. See Figure
1. Locknut, Adjustable Idler Gear (3)
4. Idler Hub, Adjustable
2. Retaining Plate, Adjustable Idler Gear Hub
5. Gear Case
3. Gear Assembly, Adjustable Idler
6. Stud, Adjustable Idler Gear (3)
Adjustable Idler Gear and Related Parts
The adjustable idler gear is pressure lubricated by engine oil fed to a gallery drilled into the gear case. This gallery indexes with the cylinder block oil gallery. See Figure
Adjustable Idler Gear Oil Gallery Location
The adjustable idler gear bushing has a series of machined grooves in the contact surface, for oil retention. The bushing is not serviced separately. If the bushing becomes worn or damaged, the gear and bushing must be replaced as an assembly.
There are three bolt holes in the hub where it is inserted over the studs. See Figure
Adjustable Idler Gear Bolt Hole Location
The top two holes are elongated, to allow the idler gear and hub assembly to be moved in relationship to the camshaft drive gear. The bottom stud hole is not elongated, and is a close fit to the stud. This allows the adjustable idler gear to pivot on the bottom stud, so the adjustable idler gear to camshaft drive gear lash can be adjusted without changing the clearance between the adjustable idler gear and camshaft idler gear. The adjustable idler gear retaining plate has a flat on the bottom to clear the bull gear for removal and installation. See Figure
Adjustable Idler Gear Retaining Plate
Repair or Replacement of Adjustable Idler Gear Assembly
To determine if repair or replacement of the adjustable idler gear assembly is necessary, perform the following procedure. See Figure
Flowchart for Repair or Replacement of Adjustable Idler Gear Assembly
In order to maintain the proper timing between the crankshaft and the camshaft, a series of timing marks are stamped or etched on the gears in the gear train. With the timing marks aligned, the gears can be replaced exactly as removed.
1. Idler Gear, Camshaft
4. Bull Gear
2. Idler Gear, Adjustable
5. Timing Gear, Crankshaft
3. Drive Gear, Camshaft
Engine Gear Train and Timing Marks
Remove the adjustable idler gear assembly as follows:
Always use crankshaft protector, J 35994
, to guard against damage to the oil seal area of the crankshaft. When removing the bull gear or camshaft idler gear and hub assembly, do not come in contact with the oil seal contact surface of the crankshaft. If sealing surface is scratched, an oil leak may result.
Install J 35994
, to the oil seal contact area of the crankshaft.
Working through the four access holes in the bull gear and camshaft idler assembly, remove two of the four bolts that secure the bull gear and camshaft idler gear hub to the cylinder block. See Figure
Removing Bull Gear and Camshaft Idler Gear Hub
Install J 35785
, to the holes from where the bolts were removed.
Remove the remaining two bull gear and camshaft idler gear hub bolts.
Grasp the bull gear and remove the bull gear and camshaft idler gear and hub assembly from its recess in the cylinder block.
Remove the three adjustable idler gear flanged locknuts.
Remove the adjustable idler gear hub retaining plate.
Remove the adjustable idler gear and hub.
Inspection of Adjustable Idler Gear Assembly
Inspect the adjustable idler gear assembly as follows:
Wash the adjustable idler gear, hub, and retaining plate thoroughly in clean fuel oil.
To avoid injury from flying debris when using compressed air, wear adequate eye protection (face shield or safety goggles) and do not exceed 40 psi (276 kPa) air pressure.
Dry with compressed air.
Examine the gear teeth for evidence of scoring, pitting and wear.
If gear teeth are damaged, also inspect the other gears in the gear train.
If severely damaged or worn, replace the gear.
If no damage is found, reuse the gear.
Inspect the contact surface of the hub for scoring or evidence of overheating (blue discoloration).
If hub has blue discoloration, replace the hub.
If hub has no blue discoloration, reuse the hub.
If slight irregularities are present, use a fine stone or emery cloth to remove them.
Check the lubrication hole and gallery in the gear case for blockage.
If the lubrication hole is blocked, clear the lubrication hole.
If the lubrication hole is not clogged, no cleaning is required.
Inspect the bushing contact surface of gear and bushing assembly for signs of scoring, discoloration due to overheating, or excessive wear.
If the surface of the bushing is not acceptable, replace the gear and bushing as an assembly.
If the surface has no damage, reuse the bushing assembly.
Measure the clearance between the bushing and hub.
If the clearance is more than 0.033 - 0.076 mm (0.0013 -0.0030 in.), replace the gear and bushing as an assembly.
If the clearance is to specification, 0.033 - 0.076 mm (0.0013 -0.0030 in.), reuse the gear and bushing assembly.
Installation of Adjustable Idler Gear Assembly
Install the adjustable idler gear and related parts as follows:
Coat the contact surfaces of the hub and idler gear bushing with clean engine oil.
Install the hub, with the word "OUT" facing outward, to the three studs in the gear case with the oil supply hole in the hub towards the gear case.
Align the timing marks on the face of the adjustable idler gear and camshaft drive gear and install the adjustable idler gear to its hub. See Figure
Coat the bearings and contact surfaces of the bull gear assembly with clean engine oil.
Looking through the inspection hole in the bull gear, align the timing marks on the camshaft idler gear (mounted to the rear of the bull gear) with the adjustable idler gear. Align the timing marks on the bull gear and crankshaft timing gear. Refer to section
. Install the bull gear hub assembly to the cylinder block. See Figure